Recording method for a magneto-optical recording medium for position adjustment of a magnetic head

ABSTRACT

A reading method for a magneto-optical recording medium is provided, irradiating laser light as a reading beam and using a magnetic head. High density and high transmission rate are possible and a correct reading can be performed according to the length of recording marks by reading the magneto-optical recording medium while impressing a magnetic field with an orientation promoting the translation of magnetic domain walls. In the magnetic super resolution type magneto-optical recording medium, which attains a signal only from one portion of the irradiation domain of the reading beam and has at least a recording layer and a reading layer on a substrate, the focused laser light is irradiated as a reading beam and the magnetic field is modulated, using the magnetic head, which is equipped with a slider and glides or floats on the recording medium. The magneto-optical recording medium is read, while impressing a magnetic field 161 that accelerates at least the transcription of the magnetization of the recording layer into the reading layer.

“This application is a Divisional of application Ser. No. 08/883,549,now U.S. Pat. No. 5,986,977 filed Jun. 26, 1997, which application(s)are incorporated herein by reference.”

FIELD OF THE INVENTION

This invention relates to an optical recording medium used for recordingand reading of information, and to a recording/reading method for such arecording medium. This invention can be applied to optical information,acoustical information, computer data, or multimedia files that combinethese types of information.

BACKGROUND OF THE INVENTION

In recent years, recording media such as CD, LD, MD, 3.5″ data files,5.25″ data files and PD have achieved practical use as a recordingmedium for optical information, acoustical information, or computer dataand the like. In the course of our progress towards information society,an optical recording/reading medium that combines high density, highcapacity, and high speed is in demand. In this respect, amagneto-optical recording medium with a magnetic induction type superresolution technique has caught attention as a technique that exceedsthe resolution of a light beam, and is expected to become a coretechnology for future high density optical recording media. Suggestionsconcerning this matter can be found in the Publication of UnexaminedPatent Application Nr. Hei 03-242845 among others. Furthermore, it hasbeen suggested to achieve an even higher density for recording/reading,through combined use of the super resolution technique and a magneticmodulation recording technique, which allows easy recording ofmicro-marks. Publication of Unexamined Patent Application Nr. Hei03-242845 also makes suggestions concerning this matter.

Referring to FIG. 19, an example of a prior art super resolutiontechnique is explained below. First of all, the information is recordedusing a known recording technique, such as light modulation or magneticmodulation. The recorded information is stored in a recording layer 7.When the information is read, the recording medium moves in arrowdirection A. Preceding the reading, the magnetization of a reading layer5 is already oriented in one direction by an initializing magneticimpression means 8. A reading beam is focused, and an irradiation domain1 is irradiated. Together with the reading beam irradiation, the readinglayer 5 is heated. When the temperature rises due to the heating, theexchange coupling force acting in the recording layer 7 and the readinglayer 5 grows stronger, and a magnetic domain recorded in the recordinglayer 7 is transcribed into the reading layer 5 via an intermediatelayer 6. Moreover, in the high temperature domain, the intermediatelayer 6 exceeds the Curie point, the magnetic coupling between therecording layer 7 and the reading layer 5 is interrupted, and themagnetization of the reading layer 5 is oriented into one direction by areading magnetic field impression means 9. In other words, in the beamirradiation domain 1, a low temperature mask domain 2 and a hightemperature mask domain 3 become the masked state in order to orient themagnetization into a fixed direction unaffected by the recordedinformation. Hence, when the information is read, the magnetic domainsof the recording layer 7 are transcribed into the reading layer 5 in anaperture domain 4 only. Consequently, it is possible to enlargeconsiderably the resolution, which was previously determined by the sizeof the light beam irradiation domain 1.

In order to improve the high resolution performance as an effect of thissuper resolution reading technique even further, a joint use of magneticmodulation, allowing an easy recording at higher density, has beensuggested. Publication of Unexamined Patent Application Nr. Hei03-242845 makes suggestions concerning such matter.

However, the above configuration has posed several problems, which shallbe described below.

(1) When the magnetization of the aperture domain 4 of the reading layer5 is reversed according to the magnetization of the recording layer 7,the translation of the magnetic domain wall is not that fast. For thatreason, although the magnetization of the aperture domain 4 of thereading layer 5 reverses quickly in the direction of the magnetic fieldthat is impressed by the reading magnetic field impression means 9, thereversal in the other direction becomes slow. Not only does this lead toa distortion of the reading wave form, but it also enlarges the edgeshift for a mark edge recording with a higher density recording.Furthermore, if the linear velocity is raised to accelerate the transferrate, this drawback becomes even more severe. Consequently, this posesan obstacle on the way to higher density and higher transfer rate.

(2) To initialize the magnetization of the reading layer 5 into anorientation in one direction, a large magnetic field in initializingmagnetic impression means 8 is necessary.

(3) Preceding the magnetic modulation recording, anticipatory positionadjustment has to be performed in order to locate the magnetic field inthe focused laser spot effectively.

(4) If the temperature changed after the initialization, or tiltoccurred due to humidity variation, then it was difficult to performrecording/reading/erasure with the most suitable operation power.

(5) Based on magnetic field modulation recording, overwriting is ofcourse possible, and in the case of a high density recording, it is agreat advantage that the recording power margin is very broad. This isto avoid a condition of neighboring marks resembling overlappingcircles, because in magnetic field modulation recording, the recordingoccurs while the portion of the mark that has just been formed isrepolarized. However, if a high density recording is attempted by makingthe track intervals narrow, then the broad recording power margin turnsinto a disadvantage. In other words, in the case of magnetic fieldmodulation, even with excess recording power, the recording power islikely to be set on the higher side, in order to prevent the recordingmarks from turning into an overlapping circles condition. In that case,even though the overlapping circles condition could be avoided, therehave been problems such as the enlargement of the recording mark, thedeletion of recorded marks in neighboring tracks, or the increase ofcross-talk.

(6) Hitherto, in devices for the reading of magneto-optical recordings,during short term stand-by periods for recording or reading, the focusservo and the tracking servo were operating and standing by underreading conditions. However, if the servos have to stand by underreading conditions in a magnetic super resolution type magneto-opticalrecording medium, which necessitates a reading magnetic field, there hasbeen the problem of waste through dissipation of power in theelectromagnet type magnetic head.

SUMMARY OF THE INVENTION

The present invention solves the above problems and aims at providing areading method, a recording method, and a reading/recording method of anoptical recording medium, a magneto-optical recording medium forposition adjustment of a magnetic head, a position adjustment method ofthe magnetic head using that medium, and an optical recording medium,thus enabling high densities and high transfer rates when using amagnetic induction type super resolution recording medium.

To achieve these goals, a first reading method for a magneto-opticalrecording medium is characterized in that the magneto-optical recordingmedium is read while controlling the translation of magnetic domainwalls by irradiating focused laser light as a reading beam in a magneticsuper resolution type magneto-optical recording medium that attains asignal only from one portion of the irradiation domain of the readingbeam and is provided with a recording layer and a reading layer on asubstrate, and by modulating a magnetic field by using a magnetic head,which is equipped with a slider and glides or floats on the magneticsuper resolution type magneto-optical recording medium. By taking theabove measure, a precise reading, which is responsive to the length ofthe recording mark, can be performed, and high density and high transferrate become possible.

In the first reading method for a magneto-optical recording medium, itis preferable that the magneto-optical recording medium is read whilealternating, with a period equivalent to less than ½ the shortestwavelength of the recording marks, the polarity of the magnetic fieldbetween a polarity that accelerates a transcription of the magnetizationof the recording layer into the reading layer and a polarity that delaysa transcription of the magnetization of the recording layer into thereading layer, in a portion of the beam irradiation domain from whichthe reading signal is attained. By taking this measure, it is possibleto attain a good response at both the beginning and the end of therecording marks.

Furthermore, it is preferable to read the magneto-optical recordingmedium while reversing the polarity of the reading magnetic fieldimmediately, whenever a magnetic reversal of the reading layer isdetected. By taking this measure, the signal can be read accurately,because it is possible to transcribe instantaneously the magnetizationof the recording layer into the reading layer, regardless of thebeginning or end of the recording mark.

Furthermore, it is preferable to attain the reading signal on the basisof an electric signal for driving the magnetic field during reading. Bytaking this measure, simple reading becomes possible.

In a second reading method for a magnetic super resolution typemagneto-optical recording medium of the present invention, reading isperformed by a reading light beam, while impressing a magnetic fieldwith an electromagnet type magnetic head that is equipped with a sliderand glides or floats on the magneto-optical recording medium thatattains a signal only from one portion of the irradiation domain of thereading beam. The second reading method for a magneto-optical recordingmedium is characterized in that, in a stand-by state for reading, thesame conditions as for a reading mode are maintained, but the drivingcurrent for the magnetic head is made smaller than in the reading stateand a fixed reading magnetic field is impressed when switching from thestand-by state to the reading state.

In the second reading method for a magneto-optical recording medium itis preferable that the laser power in the stand-by state for reading issmaller than the reading power and the laser power is increased when thestate of stand-by is shifted to the state of reading. By taking thesemeasures, the dissipated power can be decreased.

Next, a third reading method for a magneto-optical recording medium ofthe present invention is characterized in that: two domains, i.e. a lowtemperature portion and a high temperature portion, are masked insidethe irradiation domain of a reading beam; a double mask type superresolution magneto-optical recording medium is used, wherein the lowtemperature mask domain and the high temperature mask domain of areading layer are magnetized in opposite directions by a readingmagnetic field, regardless of the information stored in a recordinglayer; and the recorded information is read while setting the readingpower so that the reading signal level stays almost the same, regardlessof the orientation of the reading magnetic field.

In the third reading method for a magneto-optical recording medium, itis preferable to read the recorded information while impressing at leastin the direction promoting the translation of magnetic walls a magneticfield using a magnetic head that is equipped with a slider and glides orfloats on the magnetic super resolution type magneto-optical recordingmedium. By taking this measure, the most suitable reading power can beselected.

Next, in a first recording method for a magneto-optical recordingmedium, recording is performed using a magnetic head that is equippedwith a slider and glides or floats on a magnetic super resolution typemagneto-optical recording medium, after the magneto-optical recordingmedium, which attains a signal only from one portion of the irradiationdomain of the reading beam, has been initialized at room temperature,polarizing the reading layer into one direction with an externalmagnetic field. The first recording method for a magneto-opticalrecording medium is characterized in that at least a range of themagneto-optical recording medium that is bigger than the domain formedby the recording marks is already polarized in the same orientation asthe initialization at the reading time. By adopting this recordingmethod, the recording magnetic field necessary for initialization can bereduced.

Next, in a second recording method for a magneto-optical recordingmedium, a signal is recorded while, according to the signal to berecorded, a magnetic field is modulated with a magnetic head that isequipped with a slider and glides or floats on a magnetic superresolution type magneto-optical recording medium that attains a signalonly from one portion of the irradiation domain of the reading beam. Thesecond recording method for a magneto-optical recording medium ischaracterized in that in an operation to perform a test-writingpreceding the recording, a deletion operation is performed byirradiating continuous light while impressing a constant deletionmagnetic field; after the deletion operation, test-writing is performedwith a mark pitch that is smaller than a track pitch, while changing thepower for recording through light modulation; and a recording poweravoiding a condition of the recording marks resembling overlappingcircles is determined through the test-writing. By adopting such arecording method, it is possible to prevent an increase of cross-talk ordeletion of marks in neighboring tracks.

In the second recording method for a magneto-optical recording medium,it is preferable that: information is recorded with a magnetic fieldthat is modulated according to the information to be recorded, using alight pulse with a constant period T1 that is synchronized to the clocksignal; after the deletion operation, in a constant magnetic fieldpointing in the opposite direction of the deletion magnetic field or inan alternating field with a period T2 (with 2 T1≧T2>T1), the recordingis performed through a light pulse with a period T2, which issynchronized to the clock signal, matching the timing with which amagnetic field is impressed in the opposite direction of the deletionmagnetic field while the light amount of the recording light pulse ischanged; the most suitable light amount is sought on the basis of theresult of reading; and the recording is performed with the most suitablelight amount, using a modulation magnetic field carrying the informationto be recorded and a light pulse with the period T1.

In a disk-shaped magneto-optical recording medium for positionadjustment of a magnetic head of the present invention, themagnetization direction of a portion of a reading layer in theirradiation domain of a reading beam is determined by an external field.The disk-shaped magneto-optical recording medium for position adjustmentof a magnetic head is characterized in that the magneto-opticalrecording medium has an eccentricity of more than 50 μm. In such arecording medium, precise position adjustment can be performed easily.

It is preferable that the disk-shaped magneto-optical recording mediumfor position adjustment of a magnetic head comprises a reading layer, anintermediate layer, and a recording layer on a substrate, and that theCurie point of the intermediate layer is set lower than the Curie pointsof the reading layer and the recording layer.

Next, in a method for position adjustment of a magnetic head of thepresent invention, the magnetization direction of a portion of a readinglayer in the irradiation domain of a reading beam is determined by anexternal field and a disk-shaped magneto-optical recording medium isused that has an eccentricity of more than 50 μm. The method forposition adjustment of a magnetic head is characterized in that: whenthe position of laser irradiation and the position of the magnetic fieldimpression are matched, a focus servo and a tracking servo for thefocused laser light in the rotating magneto-optical recording medium areoperated, and a device is used to record or read while modulatingfocused laser light and a magnetic field with a magnetic head that isequipped with a slider and glides or floats on the magneto-opticalrecording medium; and the magnetic head is adjusted to the most suitableposition by observing the reading signal while the magnetic head ismoved over the surface of the magneto-optical recording medium, and themodulated magnetic field is impressed. By adopting such a method forposition adjustment, precise position adjustment can be performedeasily.

In the method for position adjustment of a magnetic head, it ispreferable that a reading layer, an intermediate layer, and a recordinglayer are disposed on a substrate of the optical recording medium, andthe Curie point of the intermediate layer is set lower than the Curiepoints of the reading layer and the recording layer.

An optical recording medium, comprising a recording layer and a readinglayer on a substrate and in which binary information expressed by “1”sand “0”s is recorded in the recording layer, is characterized in that:the optical recording medium has at least two different temperaturedomains, the two temperature domains being a first temperature domainwherein the optical characteristics of the reading layer changeresponding to the information stored in the recording layer, and asecond temperature domain wherein the optical characteristics of thereading layer are constant regardless of the information stored in therecording layer; either the first temperature domain or the secondtemperature domain includes room temperature, the other temperaturedomain being higher than room temperature; the reading is performedwhile the first temperature domain and the second temperature domain arecoexistent in the irradiation domain of the reading beam; and in therecording layer, the optical recording medium has a power calibrationdomain where only “1”s or “0”s are recorded in periodically fixedsections.

It is preferable that the above optical recording medium according,comprises a power calibration domain in each smallest recording unit.

Furthermore, it is preferable that in the above optical recordingmedium, a relationship between a critical reading power and at least onerecommended operating power of the operating powers for recording,reading and deletion, or the information to calculate the relationshipis stored in an administrative area. In such an optical recordingmedium, it is possible to perform recording/reading/deletion with themost suitable operating power, even if the temperature varies from thetemperature at initialization time, or if tilt occurs due to humidityvariations.

Next, a recording/reading method for an optical recording medium of thepresent invention is characterized in that: the optical recording mediumcomprises a recording layer and a reading layer on a substrate; binaryinformation expressed by “1”s and “0”s is recorded in the recordinglayer; the optical recording medium has at least two differenttemperature domains, the two temperature domains being a firsttemperature domain wherein the optical characteristics of the readinglayer change responding to the information stored in the recordinglayer, and a second temperature domain wherein the opticalcharacteristics of the reading layer are constant regardless of theinformation stored in the recording layer; either the first temperaturedomain or the second temperature domain includes room temperature, theother temperature domain being higher than room temperature; the readingis performed while the first temperature domain and the secondtemperature domain are coexistent in the irradiation domain of a readingbeam; the optical recording medium has a power calibration domain in therecording layer, wherein only “1”s or “0”s are recorded in periodicallyfixed sections; the reading is performed while successively changing thereading power in the power calibration domain; a critical reading power,at which the inside of the reading beam irradiation turns from thecondition of either an exclusive first temperature domain or anexclusive second temperature domain into the condition of two coexistenttemperature domains, or at which the condition of two coexistenttemperature domains turns into the condition of either an exclusivefirst temperature domain or an exclusive second temperature domain, issought; and based on the result, at least one operating power of theoperating powers for recording, reading and deletion is set.

In the above recording/reading method for an optical recording medium,it is preferable that the critical reading power is sought using thetime from the beginning of the increase in the reading power to theoccurrence of a gate signal, when the inside of the reading beamirradiation turns from the condition of either an exclusive firsttemperature domain or an exclusive second temperature domain into thecondition of two coexistent temperature domains, or the time to theoccurrence of a gate signal, when the condition of two coexistenttemperature domains turns into the condition of either an exclusivefirst temperature domain or an exclusive second temperature domain. Byadopting the above recording/reading method, it is possible to performrecording/reading/deletion with the most suitable operating power, evenif the temperature varies from the temperature at initialization time,or if tilt occurs due to humidity variations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural drawing of the recording medium used in apreferred embodiment of the present invention.

FIG. 2 shows a recorded magnetic domain arrangement according to apreferred embodiment of the present invention.

FIG. 3 is a structural drawing of the magnetic field modulationrecording device used in a preferred embodiment of the presentinvention.

FIG. 4 is a structural drawing of the disk-shaped recording medium foradjustment in a preferred embodiment of the present invention.

FIG. 5 is a structural drawing of the disk-shaped recording medium foradjustment in a preferred embodiment of the present invention.

FIG. 6 is a structural drawing of the disk-shaped recording medium foradjustment in a preferred embodiment of the present invention.

FIG. 7 is an explanatory drawing of the magnetization conditions in apower calibration domain portion in a preferred embodiment of thepresent invention.

FIGS. 8A-D show the reading signal of a power calibration domain portionin a preferred embodiment of the present invention.

FIG. 9 is an explanatory drawing of the magnetization conditions in apower calibration domain portion in a preferred embodiment of thepresent invention.

FIGS. 10A-E are explanatory drawings of the operation in the datarecording mode and in the test-writing mode in a preferred embodiment ofthe present invention.

FIGS. 11A-C are explanatory drawings of the operation of the drivingcircuit of the magnetic head in a preferred embodiment of the presentinvention.

FIG. 12 is an explanatory drawing of operation of the driving circuit ofthe magnetic head in a preferred embodiment of the present invention.

FIG. 13 is an explanatory drawing of the operation of the readingconditions in the beginning portion of a recording mark in a preferredembodiment of the present invention.

FIG. 14 is an explanatory drawing of the operation of the readingconditions in the end portion of a recording mark in a preferredembodiment of the present invention.

FIGS. 15A-B are explanatory drawings of the operation of a readingmagnetic field and a reading signal in a preferred embodiment of thepresent invention.

FIGS. 16A-B are explanatory drawings of the operation of a readingmagnetic field and a reading signal in a preferred embodiment of thepresent invention.

FIG. 17 is a structural drawing of the recording medium in a preferredembodiment of the present invention.

FIGS. 18A-B are explanatory drawings of the operation of a readingmagnetic field and a reading signal in a preferred embodiment of thepresent invention.

FIG. 19 is a principal drawing of the operation in a conventional doublemask type magnetic induction type super resolution recording medium.

DETAILED DESCRIPTION OF THE INVENTION

The following is an explanation of a preferred embodiment of the presentinvention, divided into pre-treatment of the magneto-optical recordingmedium, adjustment of the magnetic head, setting of the reading power,setting of the recording power, and a method for impression of thereading magnetic field.

(I) Pre-treatment of the Magneto-optical Recording Medium

First of all, an example of the pre-treatment of the magneto-opticalrecording medium is explained using FIG. 1 and FIG. 2. This exampleallows decreasing the magnetic field during initialization. FIG. 1 showsthe structure of the magneto-optical recording medium used in thisexample. In FIG. 1, 11 is a substrate, 12 is a dielectric film, 13 is areading layer, 14 is an intermediate layer, 15 is a supplementary layer,16 is a recording layer, 17 is a protection layer, and 18 is an overcoatlayer. The layers from the reading layer 13 to the protection layer 17are formed successively through sputtering film formation on thesubstrate, and the overcoat layer is formed subsequently through spincoating.

Next, the pre-treatment of a magneto-optical recording medium with sucha construction is explained. The pre-treatment is performed withmagnetic field modulation after preparation of the magneto-opticalrecording medium, and before the recording of data. In this example, itis advantageous that a magnetic head is used for the recording, equippedwith a slider and gliding or floating on the magnetic super resolutiontype magneto-optical recording medium, which attains a signal only fromone portion of the irradiation domain of the reading beam, and after aninitialization is performed at room temperature, magnetizing the readinglayer in one direction with an external magnetic field. To be concrete,preceding the recording, a range wider than the domain formed by atleast the recording marks of the magneto-optical recording medium isalready polarized in the same direction as the initialization at thereading time. In other words, as can be seen from the recorded magneticdomain arrangement of FIG. 2, a magnetic field is applied in the samedirection as the initialization magnetic field at the reading time, overthe range of Wi, which is wider than the recording width Wr of arecorded magnetic modulation. In this example, the pre-treatment wasperformed through photo-thermal magnetic recording, using a focus servoand a tracking servo operated with a constant laser power that was up to20% bigger than during the recording of the magnetic modulation, whilethe recording magnetic field was facing in the same direction as theinitialization magnetic field at the reading time. By doing so, of thetwo types of magnetic domains (upwards oriented and downwards oriented)formed through recording with magnetic field modulation, all themagnetic domains that have to be reversed through the initialization canbe formed as isolated recording marks afterwards. As a result, it waspossible to cut the recording magnetic field necessary forinitialization in half. In a test sample that has not been subjected toinitialization, an initialization field of 7 kilo-oersted was necessaryfor long marks with 4 μm mark length. On the other hand, through theintroduction of the pre-treatment according to the present example, aninitialization with 4 kilo-oersted was possible.

If it is necessary to arrange the orientation of the magnetization ofthe reading layer in only one direction at room temperature beforeirradiation with a reading beam, or in other words, if it is necessaryto perform initialization, then the pre-treatment is an effective meansfor any magnetic induction super resolution recording medium recordingmagnetic field modulation.

Even if the operation of deletion before the recording is a conventionalmethod in the recording of light modulation, a large magnetic fieldduring initialization is not necessary, because the recording marks areformed in an isolated condition. However, in the recording of magneticmodulation, the concept of deletion before the recording isunconventional, because overwriting is possible. Furthermore, if thepre-treatment according to this procedure is performed once beforeshipment, it does not have to be repeated for every overwriting, andthus does not burden the user.

In this example, photo-thermal magnetic recording was performed as ameans for the pre-treatment, as described above. A focus servo and atracking servo were operated with constant laser power that was up to20% bigger than during the recording of the magnetic modulation, whilethe recording magnetic field was facing in the same direction as theinitialization magnetic field at the reading time. However, the goal wasreached, because this pre-treatment produces recording marks that areformed by recording of magnetic modulation, and are initialized at thereading time in an isolated condition. Consequently, it is alsoadvantageous that eventually a magnetic field stronger than the coercivefield strength of the recording layer polarizes the entire disk surfacein the initialization direction at the time of reading. Alternatively,it is also advantageous that, under a magnetic field in theinitialization direction at the time of reading, a flash lampirradiation heats up and polarizes the entire recording layerinstantaneously.

(II) Adjustment of the Position of the Magnetic Head

Next, an example of the adjustment of the position of the magnetic headis explained using FIGS. 3 to 5. Generally, in the case of a magneticfield modulation recording, a device with a structure such as shown inFIG. 3 is used. In FIG. 3, 31 is a magneto-optical recording medium, 32is an optical head, 33 is a magnetic head, and 34 is a slider. In orderto modulate the magnetic field rapidly, the magnetic head for magneticfield modulation recording is small and the effective range of themagnetic field applied by magnetic head 33 is even smaller. Therefore,preceding the magnetic field modulation recording, a position adjustmentis performed to locate the magnetic field in the focused laser spoteffectively.

Below, a method for effective position matching of the magnetic head andthe optical head is explained. The method for effective positionmatching of the magnetic head and the optical head that has beenperformed in this example is advantageous to match the laser irradiationposition with the magnetic field impression position in a device forrecording or reading while the magnetic field is modulated using afocused laser and a magnetic head, which is equipped with a slider andglides or floats on the magneto-optical recording medium. In thisexample, the magnetization direction of a portion of the reading layercovering at least the irradiation domain of the reading beam isdetermined by an external magnetic field. Furthermore, a disk-shapedmagneto-optical recording medium is used, having an eccentricity of morethan 50 μm. While this magneto-optical recording medium is rotated, thefocus servo and the tracking servo of the focused laser light areoperated, and the magnetic head is adjusted into the most suitableposition by observing the reading signal while the magnetic head ismoved along the surface of the magneto-optical recording medium and themodulated field is impressed.

FIG. 4 shows the disk-shaped recording medium for adjustment, asaccording to this example. On a substrate 11, a dielectric film 12, areading layer 13, an intermediate layer 14, a recording layer 16, aprotection layer 17, and an overcoat layer 18 are formed successively.The Curie point of the intermediate layer 14 is set lower than the Curiepoints of both the reading layer 13 and the recording layer 16, so thatonly the intermediate layer 14 rises above the Curie point in a portionof the beam irradiation domain at the reading time, and the exchangecoupling between the reading layer 13 and the recording layer 16 isinterrupted. Consequently, when the exchange coupling between thereading layer 13 and the recording layer 16 is interrupted, thepolarization of a portion of the reading layer 13 is determined by anexternal magnetic field. The use of an optical recording medium withsuch a structure, simply in order to adjust the position of the magnetichead, has been suggested in Publication of Unexamined Patent Appl. Nr.Hei 08-017090, and is thus well known. In the present example, themagneto-optical recording medium differs from the prior art, in that thedeviation of the track center from the center of the center hole, i.e.the eccentricity X, exceeds 50 μm, as is shown in FIG. 5. The reason whythe eccentricity X exceeds 50 μm is that in a conventional opticalrecording medium, a maximum eccentricity of 50 μm is the standard, andfor any recording medium within this standard it is necessary to makesure that there is no problem with a larger eccentricity in order toimpress a magnetic field effectively. If such a recording medium isused, then the laser beam sways over at least 100 μm in a radialdirection relative to the recording medium, when the focus and thetracking servo move the focused laser beam over the recording medium.Moreover, if eccentricity X is inside the range followed by the trackingservo, then the tracking servo will not operate smoothly if this rangeis too big. Because the tracking servo becomes unstable when the regulareccentricity is over 150 μm, an eccentricity X in the range 50-150 μm ispreferable.

With the focus and the tracking servo in operation, the opticalrecording medium shown in FIG. 4 is read while impressing a modulatedmagnetic field with a magnetic head 33, which is equipped with a sliderand glides or floats on the recording medium, and the reading signal isattained only from the portion of the beam irradiation domain in whichthe reading layer 14 is above the Curie point. Because the focused beamsways over at least 100 μm due to the eccentricity of the recordingmedium, a position of the magnetic head covering at least a range of 100μm effectively can be easily found by moving the magnetic head in aradial direction relative to the recording medium. By subsequentlymoving the magnetic head in a circumferential direction relative to therecording medium, it is possible to find the most suitable position anddecide the magnetic head's position.

Moreover, this series of adjustments is usually performed during theassembly of the drive, but it can also be applied to resolutioncorrection or readjustment after assembly and the like, should the needarise.

Moreover, in this example, an optical recording medium with a magneticinduction type super resolution (a so-called FAD) was used, but it isthe same for a recording medium with a structure as shown in FIG. 1. Inother words, it is possible to use a disk-shaped magneto-opticalrecording medium having an eccentricity of more than 50 μm in which themagnetization of at least the portion of the reading layer in theirradiation domain of the reading beam is determined by an externalfield.

(III) Setting the Magneto-optical Recording Medium and its Reading Power

Next, an example of the method of setting of the magneto-opticalrecording medium and its reading power is explained using FIGS. 6-9. Itis a goal of this example to perform recording/reading/deletion with themost suitable operating power, even if the temperature varies from thetemperature at initialization time, or if tilt occurs due to humidityvariations and the like.

The optical recording medium according to this example has at least arecording layer and a reading layer on a substrate, and in the recordinglayer binary information is stored, represented by “1”s and “0”s. Theoptical recording medium according to this example is furthercharacterized in that:

(a) The optical recording medium has at least two different temperaturedomains, i.e. a first temperature domain wherein the opticalcharacteristics of the reading layer change responding to theinformation stored in the recording layer, and a second temperaturedomain wherein the optical characteristics of the reading layer areconstant, regardless of the information stored in the recording layer.

(b) Either the first temperature domain or the second temperature domainincludes room temperature, the other temperature domain being higherthan room temperature.

(c) The reading is performed while the first temperature domain and thesecond temperature domain are coexistent in the irradiation domain ofthe reading beam.

(d) The optical recording medium has a power calibration domain in therecording layer of the optical recording medium, wherein only “1”s or“0”s are recorded periodically in fixed sections.

With the help of the drawings, the specific aspects are explained below.In FIG. 6, 31 is an optical recording medium, 62 are recording tracks,and 63 are power calibration domains, wherein only “1”s or “0”s arerecorded in periodically fixed sections. These are employed in eachsector constituting a minimal recording unit. The recording mediumcomprises at least a substrate, a recording layer and a reading layer,and binary information, represented by “1”s and “0”s, is stored in therecording layer. The optical recording medium used in this example isformed in succession by a substrate, a dielectric film, a reading layer,a supplementary layer, a recording layer, a protection layer, and anovercoat layer.

As is shown in FIG. 7, in a portion of the power calibration domain, therecording layer 16 is magnetized in an upwards direction throughout thefigure, a magnetic domain wall is formed by the supplementary layer 15,and in a second temperature domain T2 including room temperature, thereading layer is magnetized in a downward direction. This can berealized easily by forceful orientation in a downward direction with anexternal initializing magnetic field, and consequently the opticalcharacteristics of the reading layer, i.e. the direction of the Kerrrotation, are constant regardless of the information stored in thesecond temperature domain T2.

On the other hand, in the heated first temperature domain T1, thecoercive field strength of the reading layer 13 drops whereas theexchange coupling force between the recording layer 16 and the readinglayer 13 rises, and the magnetization of the recording layer 16 istranscribed. As a result, the magnetization of the reading layer 13follows the magnetization of the recording layer 16. In other words, theoptical characteristics, i.e. the orientation of the Kerr rotation ofthe reading layer, change according to the information stored in thefirst temperature domain T1 in the recording layer.

The power calibration performed in this example, which uses thepreviously described optical recording medium has the followingcharacteristics:

(a) The reading is performed while successively changing the readingpower in the previously described power calibration domain,

(b) Inside the irradiation of the reading beam, a critical reading poweris sought, at which the condition of either an exclusive firsttemperature domain or an exclusive second temperature domain turns intothe condition of two coexistent temperature domains, or at which thecondition of two coexistent temperature domains turns into the conditionof either an exclusive first temperature domain or an exclusive secondtemperature domain, and based on the result, the operation power is setfor at least one of recording, reading, or deletion.

The situation will be explained in more detail with reference to thedrawings. FIG. 8A shows the relationship between a reading beamirradiation domain 1 and the two temperature domains, FIG. 8B shows thetransient change of laser power P until the reading power setting at thereading time is reached, FIG. 8C shows the reading signal S, which isattained in the optical head, and FIG. 8D shows the transient change oflaser power P until the recording power setting at the recording time isreached.

The reading power in power calibration domain PC is gradually increased,as is shown in FIG. 8B. However, directly before the increase of power,during the interval t1-t2, a turn-off period of 150 ns is provided, inorder to avoid the residual heat brought about by the previous readingpower irradiation. Considering the cooling time for a laser irradiatedrecording medium, this turn-off period should be longer than 100 ns.However, if the turn-off period is chosen to be too long, then theutilization rate as a recording medium drops, and the stability of theservos is harmed. Thus a turn-off period of under 1 μs is suitable. Fromt2 to t4, the reading power in power calibration domain PC is graduallyincreased. In the interval t2-t3, the extent of the irradiation domain 1of the reading beam is equal to the second temperature domain T2, as isshown in FIG. 8A. However, from t3-t4, the irradiation domain 1 turnsinto a coexistence of second temperature domain T2 and first temperaturedomain T1. At this moment, the reading signal changes abruptly in t3, asis shown in FIG. 8C. Consequently, it is possible to specify theinterval t2-t4 and, using a gate signal only open in the moment passingthrough the power calibration domain PC as well as a reference signalS1, to specify the interval t2-t3. This interval responds to sensitivityvariations occurring caused by variations of the optical head,sensitivity variations and focus deviation of the recording medium, ortilting of the optical medium or the optical head and the like.Consequently, discerning the interval t2-t3 is equivalent to seeking thecritical reading power, at which the condition of either an exclusivefirst temperature domain or an exclusive second temperature domain turnsinto the condition of two coexistent temperature domains.

Consequently, at the moment when the recording medium is inserted intothe drive, it is possible to seek with the above described method thecritical reading power simultaneously with seeking the most suitablepower for reading power, recording power, deletion power and the like,using test domains on the recording medium, and to seek the relationshipbetween the critical reading power and the various operating powers.According to the method described above, it is possible to performrecording/reading/erasure with the most suitable operation power, evenif the temperature changes after the initialization or tilt occurs dueto humidity variations, because it is possible to detect the criticalreading power Px for each sector constituting the smallest recordingunit.

As this example shows, the reading power Pr after t4 is appropriatelyset proportional to the interval t2-t3, which is equivalent to thecritical reading power Px. Similarly, in the case of recording as shownin FIGS. 8A-D, the recording power Pw after t4 is appropriately setproportional to Px. A result of recording/reading with these measureswas that a stable recording/reading/deletion, unaffected by lightmodulation recording or magnetic field modulation recording, waspossible even for variations in temperature between 20° C. and 60° C.,or variations in humidity between 40% and 80%.

Furthermore, because the relationship between the critical reading powerand the various operating powers is an inherent characteristic of therecording medium, it is advantageous to record in an administrative areathe relationship between the critical reading power and a recommendedoperating power for at least one of recording, reading and deletion, orthe information to compute these relationships. However, in this case,the manufacturer of the recording medium and the manufacturer of thedrive have to agree upon such matters as the linear velocity and thealteration velocity in the power calibration domain, and it is necessaryto revise the conditions for recording/reading in practice.

Furthermore, an example was explained, in which room temperature isincluded in the second temperature domain T2, and the first temperaturedomain T1 is higher than that. However, the present invention is notlimited to this, and the case wherein room temperature is included inthe first temperature domain T1, and the second temperature domain T2 ishigher than that, as is shown in FIG. 9, is also valid.

In this case, as shown in FIG. 9, the recording layer 16 is magnetizeduniformly upwards in a portion of the power calibration domain, and thereading layer 13 is also magnetized upwards, via the intermediate layer14, in the first temperature domain T1, which includes room temperature.

On the other hand, the exchange coupling force between the recordinglayer 16 and the reading layer 13 is interrupted, because thetemperature of the intermediate layer 14 rises above the Curie point inthe heated second temperature domain T2, and the magnetization of thereading layer 13 is forced downwards by an external magnetic field,regardless of the magnetization of recording layer 16.

In other words, the optical characteristics, i.e. the orientation of theKerr rotation of the reading layer, change according to the informationstored in the first temperature domain T1, which includes roomtemperature in the recording layer 16. On the other hand, the opticalcharacteristics of the reading layer, i.e. the orientation of the Kerrrotation, are constant regardless of the information stored in therecording layer 16 in the second temperature domain T2.

It is possible to apply the present invention to such a recordingmedium, and to find the critical reading power for each sectorconstituting a minimal recording unit with exactly the same procedure.

Furthermore, the present invention is also valid for a super resolutionrecording medium using a thin film with reflectivity and transmissivityvarying for example with temperature and not by inducing a magneticfield.

Moreover, in this example, the reading power in the power calibrationdomain was gradually increased, but the critical reading power can alsobe found by reading while gradually decreasing the reading power. Inthat case, the critical reading power becomes the reading power at whichthe condition of two coexistent temperature domains turns into thecondition of either an exclusive first temperature domain or anexclusive second temperature domain. However, considering the differencebetween the heating speed and the cooling speed of the recording medium,because the former one is faster, it is preferable that the readingpower is gradually increased.

Moreover, in this example, the reading power in the power calibrationdomains changed continuously, i.e. in an analog manner. Yet the sameeffect can be attained, even if the change is made discontinuously, i.e.in a digital manner.

Moreover, in this example, previous to changing the reading power in thepower calibration domains gradually, a turn-off period for the laser wasprovided, but this is not necessarily required, and the operating powercan be computed by using a suitable compensational term.

(IV) Setting the Recording Power

Next, an example of a method to seek the most suitable recording powerfor a recording medium as used in this example is discussed.

In conventional magnetic field modulation recording, overwriting can beperformed easily, in comparison to optical modulation recording, and inthe case of a high density recording, it is a great advantage that therecording power margin is very broad. For example, in the case ofoptical modulation recording, neighboring marks are recordedindependently, if the most suitable recording power is applied. However,when the recording power becomes excessive, the neighboring markseventually turn into a condition resembling overlapping circles. Inmagnetic field modulation recording on the other hand, the overlappingcircles condition for neighboring marks does not occur, because aportion of the marks that have just been formed is recorded while beingrepolarized.

However, if the track interval is made small, and high density recordingis attempted, then the recording power margin actually turns out to be aproblem. For example, in the case of magnetic field modulation, evenwith excessive recording power, the recording marks do not turn into anoverlapping circles condition, as has been noted above. Therefore, therecording power tends to be set on the high side. However, in this case,even if the overlapping circles condition can be avoided, it invitesproblems such as the enlargement of the recording marks, the deletion ofrecorded marks by neighboring tracks, or the increase of cross-talk. Thepresent example, which solves the above mentioned problems and can beused in a method of recording while modulating a magnetic fieldaccording to the signal to be recorded by use of a electromagnet typemagnetic head, which is equipped with a slider and glides or floats onthe magnetic super resolution type magneto-optical recording medium,which attains a signal only from one portion of the irradiation domainof the reading beam, is characterized in that:

(a) Preceding the recording, a test-writing is performed.

(b) The test-writing is performed with a mark pitch smaller than thetrack pitch, while the recording power is changed through lightmodulation, and after a deletion operation has been performed byirradiating continuous light under a constant deletion magnetic field.

(c) A suitable recording power is determined that is small enough not tolead to a drop of the reading signal accompanying recording marksresembling overlapping circles.

(d) Based on a suitable recording power for the light modulationrecording, the magnetic field modulation recording is performed.

This example is explained below, using the drawings. FIG. 10A shows thedependency of the reading signal from the recording power with magneticfield modulation and optical modulation respectively, FIG. 10B shows thewaveform of the light pulse of a magnetic field modulation recordingwhen data is recorded, FIG. 10C shows a modulation magnetic fielddriving waveform, FIG. 10D shows the waveform of the light pulse of amagnetic field modulation recording when test-writing is performed, andFIG. 10E shows the recording mark pattern attained by the test-writing,wherein Tr1 and Tr2 mark the centers of the respective neighboringtracks, TP is the track pitch, and MP is the mark pitch.

In this example, a magnetic induction type super resolution recordingmedium, as shown in FIG. 1, with a track pitch of 0.8 μm was used as arecording medium. When data is recorded in this recording medium, therecording is performed by a light pulse with a constant period T1, as isshown in FIG. 10. B, synchronized with a clock signal, under amodulation magnetic field that is proportional to the information to berecorded. The present example is characterized in that, preceding therecording, the most suitable recording power is set by an opticalmodulation recording. A method to set the most suitable recording poweris described below.

First of all, a partial deletion is performed, that can be regarded asthe test-writing. This is performed by the same method as conventionaldeletion, i.e. by irradiating laser light with constant power under aconstant magnetic field. Next, the recording is performed through alight pulse with a period T2, which is synchronized to the clock signal,as is shown in FIG. 10D, matching the timing, with which a magneticfield is impressed in the opposite direction of the deletion magneticfield in a constant magnetic field or in an alternating field with aperiod T2 (with 2 T1≧T2>T1), as shown in FIG. 10C, in the oppositedirection of the deletion magnetic field. In this example, the lattermethod was used.

By doing so, the recording marks as shown in FIG. 10E are formed. Whathas to be kept in mind here, is that if the recording power isincreased, the recording marks will become bigger as well. Consequently,if the recording power exceeds a certain value, then the neighboringmarks will turn into a condition resembling overlapping circles, and therecording signal drops. In order to prevent this, the recording powerhas to be set under a certain value, at which the neighboring marks donot turn into a overlapping circles condition. Therefore, it isnecessary to perform the test-writing with a mark pitch MP that is atleast smaller than the track pitch TP. During the test-writing, thedependence of the reading signal level S on the recording power is asshown by optical modulation recording OPr in FIG. 10A. Here, therecording power Pw, where for example the signal amplitude is thegreatest, is detected and is made the recording power when informationis recorded.

The recording power when recording information is achieved through alight pulse with the constant period T1 that has been synchronized tothe clock signal, as shown in FIG. 10B, and through the recording of amagnetic field that is modulated according to the information to berecorded, with a gliding or floating magnetic head that is equipped witha slider. The reading level S at this time has the characteristics asshown by magnetic field modulation recording MGr in FIG. 10A, and it ispossible to control the width of the recording marks, because the inputof more power than is necessary can be avoided by recording withrecording power Pw. In this example, the pulse width at the datarecording time shown in FIG. 10B was the same as the pulse width of thetest-writing shown in FIG. 10D, and the pulse period T1 was set to 2times T2. By doing so, it was possible to record for a track pitch under0.8 μm, not only the deletion rate of simple overwriting, but withoutproblems like cross-talk, deletion of neighboring tracks, even when theenvironmental temperature at the recording time varies between 20° C.and 50° C.

Furthermore, performing a test-writing with light modulation merely tomake the recording width constant, and recording of the data withmagnetic field modulation is suggested in Publication of unexaminedPatent Appl. Nr. Hei 8-7383, and thus is publicly known. However, inthis public known example the recording width is made constant merely toimprove the overwriting deletion characteristics. As opposed to that,this example aims especially at high density, and for the first time itis advantageous to make the recording width small by test-writing with amark pitch that is smaller than the track pitch, in a magnetic superresolution type magneto-optical recording medium wherein small marks canbe discriminated, by limiting the recording width in order to realize anarrow track pitch.

Furthermore, in this example, the (magnetic field modulation recording)pulse at the time of data recording, and the (optic modulationrecording) pulse at test-writing have been made to differ only in theirperiod, but in this case, because the magnetic field modulationrecording pulse period is only ½ as long, the recording mark width ofthe magnetic field modulation recording broadens due to the residualheat effect of the preceding pulse.

In order to avoid this, it is advantageous to make corrections by e.g.enlarging the pulse width at the time of test-writing with lightmodulation recording, or enlarging the bias power. For the same reason,it is advantageous to set the pulse period T2 at the time oftest-writing with light modulation recording in the range of 2T1≧T2>T1with respect to the pulse period T1 of magnetic field modulationrecording.

(V) Method for Impressing a Reading Magnetic Field when Shifting fromStand-by State to Reading State

Next, an example of a method for impressing a reading magnetic field isexplained. In conventional magneto-optical recording/reading devices,during short term stand-by periods for recording or reading, the focusservo and the tracking servo were operating, and standing by underreading conditions. However, if the servos have to stand by underreading conditions, there has been the problem of waste throughdissipated power in those devices that use a electromagnet type magnetichead.

The example of a method for impressing a reading magnetic field, whichuses a magneto-optical reading device performing reading in a light beamwhile impressing a magnetic field with a magnetic head, which isequipped with a slider and glides or floats on the magnetic superresolution type magneto-optical recording medium, which attains a signalonly from one portion of the irradiation domain of the reading beam, ischaracterized in that:

(a) In the stand-by state for reading, the same conditions as for thereading mode are maintained, but the driving current for the magnetichead is made smaller than in the reading state, and

(b) A fixed reading magnetic field is impressed, when switching from thestand-by state to the reading state.

Below, the situation will be explained in more detail with reference tothe drawings. FIGS. 11A-C illustrate the driving circuit of the magnetichead. 111 is the magnetic head, and S1, S2, S3, and S4 are switchingelements. FIG. 11A shows the condition of the circuit for the stand-bystate, FIGS. 11B and C show the condition of the circuit for the readingstate. The operation of the circuit is explained below. In the stand-bystate, S1, S2, S3, and S4 are all in an OFF position, as is shown inFIG. 11A. In order to reach the goal of the present example, it is alsovalid to put only S1 and S2 in the OFF position.

Moreover, in the stand-by state, the focus servo and the tracking servoare operating and standing by, while the laser is irradiated. The laserpower at this time can be the reading power, but, because the readingpower of a magnetic super resolution type magneto-optical recordingmedium is bigger than the reading power of a conventional recordingmedium without super resolution, it is preferable to stand by with areading stand-by power that is smaller than the reading power, and thusreduce the dissipated power.

When switching from the stand-by state to the reading state, themagnetic field is switched on by putting S1 and S4 in the ON position,as shown in FIG. 11B, or alternatively putting S2 and S3 in the ONposition, as shown in FIG. 11C, and a predetermined current flowsthrough the magnetic head 111. Furthermore, if the reading stand-bypower is made smaller than the reading power, then the laser power isincreased to the reading power, when switching from the stand-by stateto the reading state.

In this example, the dissipated during stand-by could be reduced by 1.1W compared to stand-by under reading conditions by setting the readingstand-by power to 0.7 mW, and the reading power to 2 mW, in addition tothe decrease of magnetic field driving power.

Moreover, in this example, S1, S2, S3, and S4 have all been put in theOFF position during stand-by, but it is also valid to employ a switchS5, and to put the switch S5 in the OFF position during stand-by, as isshown in FIG. 12. Furthermore, because S1, S2, S3, S4, and S5 make useof a transistor switching operation, strictly speaking, the currentflowing through the magnetic head does not necessarily become zero evenin the OFF position, since it occurs that an extremely small leakingcurrent is flowing. Even in this case, the positive results of thisexample are displayed sufficiently, because the current flowing duringstand-by is by far smaller then during reading.

(VI) Method for Impressing a Reading Magnetic Field in the Reading State

Next, an example of a method for impressing a reading magnetic field inthe reading state is explained. This example uses a magnetic superresolution type magneto-optical recording medium that attains a signalonly from one portion of the irradiation domain of the reading beam, andcomprises at least a recording layer and a reading layer on a substrate.

In this method, the focused laser light is irradiated as the readingbeam, and the magneto-optical recording medium is read, while themagnetic field is modulated using a magnetic head, which is equippedwith a slider and glides or floats on the recording medium, to controlthe translation of the magnetic domain walls. Two examples of thismethod are explained below.

The first example is characterized in that, in the above mentionedreading method, a magnetic field is alternated with a period equivalentto less than ½ the shortest wavelength of the recording marks, andreading is performed while impressing, in one portion of the beamirradiation domain from which the reading signal is attained, magneticfields of two polarities, alternatingly in the beginning and the end ofthe recording marks, i.e. a magnetic field of a polarity thataccelerates the transcription of the magnetization of the recordinglayer into the reading layer, and a magnetic field of a polarity thatinhibits the transcription of the magnetization of the recording layerinto the reading layer. The second example is characterized in that, inthe above mentioned reading method, reading is performed while reversingthe polarity of the reading magnetic field immediately, whenever amagnetic reversal of the reading layer is detected.

Below, the situation will be explained in more detail with reference tothe drawings. FIG. 13 illustrates the reading condition in the beginningportion of a recording mark during reading of a magnetic superresolution type magneto-optical recording medium that attains a signalonly from one portion of the irradiation domain of the reading beam. Therecording medium is similar to the recording medium shown in FIG. 1.

In FIG. 13, (a1), (a2), and (a3) show the relationship between recordingmarks stored in recording layer 16 and the reading beam 1, forsuccessive points in time. Inside the reading beam irradiation domain 1,the reading layer 13 is magnetized in a fixed direction in a lowtemperature mask portion 2 and a high temperature mask portion 3, whichdo not contribute to the reading signal, since only aperture portion 4contributes to the reading signal. (b1), (b2), and (b3) illustrate themagnetization of reading layer 13, intermediate layer 14, supplementarylayer 15 and recording layer 16 when an upward initialization magneticfield and a downward reading magnetic field 9 have been impressed, forthe same successive points in time as are shown in (a1), (a2), and (a3).(c1), (c2), and (c3) show the direction of the magnetization of theabove mentioned layers for successive points in time, when an upwardreading magnetic field 9 has been applied under similar conditions.

Below, the situation is explained in chronological order. In state (a1),the magnetization of recording layer 16 is transcribed in apertureportion 4 to reading layer 13 by exchange coupling between recordinglayer 16 and reading layer 13, as is shown in (b1) and (c1), and themagnetization of reading layer 13 is turned upwards. If the readingmagnetic field 9 faces downwards, then the beginning of the recordingmark approaches aperture portion 4, as is shown in (a2), and amagnetization reversal portion 131 is created in aperture portion 4 ofthe reading layer 13 due to the transcription from the recording layer16, as is shown in (b2). As time passes, the magnetization reversalportion 131 expands, and in state (a3) the magnetization of almost allof the aperture portion is reversed, as is shown in (b3). This occursbecause the magnetic domain walls expand due to the exchange couplingforce from recording layer 16 into reading layer 13, but because thereading magnetic field is applied in a direction promoting thetranslation of magnetic domain walls, these transcriptions are performedsmoothly in an extremely short time interval.

However, if the reading magnetic field points upwards, then the magneticdomain walls expand due to the exchange coupling force from therecording layer 16 into the reading layer 13, and the reading magneticfield is applied in a direction inhibiting the translation of magneticdomain walls. Therefore, the expansion speed of the magnetic domainwalls lags behind the passage of the magnetic domain walls of therecording layer, even though a magnetization reversal portion 131′ isformed, as is shown in (c2) and (c3), and this leads to a reading signalwith rather poor response.

As a result, even though the response to the beginning of the recordingmark in a downward pointing reading magnetic field is excellent, theresponse characteristics in an upward pointing reading magnetic fieldare poor.

Conversely, FIG. 14 illustrates the reading condition in the end portionof a recording mark during reading of a magnetic super resolution typemagneto-optical recording medium that attains a signal only from oneportion of the irradiation domain of the reading beam. In FIG. 14, (a1),(a2), and (a3) show the spatial relationship between recording marksstored in recording layer 16 and the reading beam 1, for successivepoints in time. (b1), (b2), and (b3) illustrate the magnetization ofreading layer 13, intermediate layer 14, supplementary layer 15 andrecording layer 16 when an upward initialization magnetic field and adownward reading magnetic field 9 have been impressed, for the samesuccessive points in time as are shown in (a1), (a2), and (a3). (c1),(c2), and (c3) show the direction of the magnetization of the abovementioned layers for successive points in time, when an upward readingmagnetic field 9 has been impressed under similar conditions.

Below, the situation is explained in chronological order. In state (a1),the magnetization of recording layer 16 is transcribed in apertureportion 4 to reading layer 13 by exchange coupling between recordinglayer 16 and reading layer 13, as is shown in (b1) and (c1), and themagnetization of reading layer 13 turns downwards. If the readingmagnetic field 9 faces upwards, then the end of the recording markapproaches aperture portion 4, as is shown in (a2), and a magnetizationreversal portion 141 is created in aperture portion 4 of the readinglayer 13 due to the transcription from the recording layer 16, as isshown in (c2). As time passes, the magnetization reversal portion 141expands, and in state (a3) the magnetization of almost all of theaperture portion is reversed, as is shown in (c3). This occurs becausethe magnetic domain walls expand due to the exchange coupling force fromrecording layer 16 into reading layer 13, but because the readingmagnetic field is applied in a direction promoting the translation ofmagnetic domain walls, these transcriptions are performed smoothly in anextremely short time interval.

However, if the reading magnetic field points downwards, then themagnetic domain walls expand due to the exchange coupling force fromrecording layer 16 into reading layer 13, and the reading magnetic fieldis applied in a direction inhibiting the translation of magnetic domainwalls. Therefore, the expansion speed of the magnetic domain walls lagsbehind the passage of the magnetic domain walls of the recording layer,even though a magnetization reversal portion 141′ is formed, as is shownin (b2) and (b3), and this leads to a reading signal with rather poorresponse.

As a result, even though the response to the beginning of the recordingmark in an upward pointing reading magnetic field is excellent, theresponse characteristics in a downward pointing reading magnetic fieldare poor.

To summarize, a comparison of FIG. 13 and FIG. 14 can teach thefollowing:

(a) If the reading magnetic field points downwards, then the beginningof a recording mark shows good response characteristics. As opposed tothat, the response characteristics at the end of the recording mark turnpoor.

(b) On the other hand, if the reading magnetic field points upwards,then the end of a recording mark shows good response characteristics. Asopposed to that, the response characteristics at the beginning of therecording mark turn poor.

Using the above results, reading was performed in this example whilealternating a magnetic field with a period equivalent to less than 112the shortest wavelength of a recording mark. By doing so, magneticfields of two polarities are impressed alternatingly with great speed inthe beginning and the end of the recording marks, and even though thetranslation of magnetic domain walls is slow in a reading field with oneof the two polarities, the magnetization of the recording layer istranscribed instantaneously, when the reading magnetic field with theother polarity is applied.

FIG. 15A shows the transient change of a reading signal S, when readingis performed with a reading magnetic field always pointing in samedirection, and FIG. 15B shows the transient change of a reading signalS, when the magnetic field is alternating. In the case of reading with areading magnetic field always pointing in same direction, either afalling response (at the beginning of the recording marks) or a risingresponse (at the end of the recording marks) becomes poor (in theexample shown in FIG. 15A, a rising response is poor), but by adoptingthe present example, good transition characteristics could be attainedfor both a falling response (at the beginning of the recording marks)and a rising response (at the end of the recording marks).

Next, a second example is explained in more detail using the drawings.In this example, the same recording medium as in the first example isused. FIG. 16A shows the transient change of the waveform of a readingsignal S, and FIG. 16B shows the transient change of a driving magneticfield H during reading. The waveform of the reading signal 163 changesabruptly when the beginning portion of a mark is detected, as is shownby 163 a. After a crossing of slice level S2 has been detected, thepolarity of the reading magnetic field changes immediately, as is shownby 161 in FIG. 16B. This brings about a level variation L at the time T0of changing the magnetic field, because the magnetization of the readinglayer of the high temperature mask portion 3 reverses. When the endportion of the mark is reached after translating the recording medium,the reading signal again changes abruptly, as is shown by 163 b. Thistime, after a crossing of slice level S3 has been detected, the polarityof the reading magnetic field changes immediately, as is shown by 161 inFIG. 16B.

If the driving waveform of the reading magnetic field does not changeuntil reference as in 162, then the reading signal turns out as shown by164. In this case, the recording mark is detected as unduly long,because the translation of the magnetic domain walls of the recordinglayer in the end portion of the mark cannot keep up with the transitspeed of the recording medium. However, if the present example isadopted, the signal can be read correctly, because the magnetization ofthe recording layer can be transcribed instantaneously into the readinglayer, regardless of the beginning or end portion of the recording mark.

Furthermore, in the reading method of this example, the reading signalis attained on the basis of the electric signal of the driving magneticfield during reading. Therefore, convenient reading is possible.

Next, in this second example, the performance of a similar reading usinganother recording medium is explained with the help of FIGS. 17 and 18.A structure shown in FIG. 17 was used as a recording medium. In FIG. 17,a controlling layer 171 is located between recording layer 16 andreading layer 13. The recording layer 16 and the reading layer 13 aremade of a ferrimagnetic film, wherein the magnetization of a transitionmetal is dominant (TM-rich), whereas the controlling layer 171 is madeof a ferrimagnetic film, wherein the magnetization of a rare earth metalis dominant (RE-rich). Furthermore, a structure is provided in which theexchange coupling force between the recording layer 16 and thecontrolling layer 171 is comparatively weak, the exchange coupling forcebetween the reading layer 13 and the controlling layer 171 iscomparatively strong, and the Curie point of the controlling layer 171is set lower than the Curie point of the other magnetic layers.

The recorded information is stored in recording layer 16, and at roomtemperature the controlling layer 171 is polarized pointing downwards bya reading magnetic field 9 in the case of the orientation of the exampleshown in FIG. 17. Thus, the reading layer 13 is magnetized pointingupwards as a total magnetization, because in the controlling layer 171the magnetization of a rare earth metal is dominant (RE-rich) and in thereading layer the magnetization of a transition metal is dominant(TM-rich). The low temperature mask portion 2 is formed due to thisphenomenon.

When the temperature rises due to irradiation with the reading beam, theexchange coupling force between recording layer 16 and controlling layer171 increases, and in the aperture portion 4, the magnetization of therecording layer 16 is transcribed into the reading layer 13 via thecontrolling layer 171. On the other hand, because the controlling layer171 loses magnetism when exceeding the Curie point, the exchangecoupling force between the recording layer 16 and the reading layer 13ceases, the reading layer 13 is magnetized pointing downwards followingthe orientation of the reading magnetic field 9, and the hightemperature mask portion 3 is formed. Consequently, high temperaturemask portion 3 and low temperature mask portion 2 are reversed togetherdue to reading magnetic field 9. Furthermore, it is always possible toarrange opposite orientation for the magnetization of the reading layer13 in the high temperature mask portion 3 and in the low temperaturemask portion 2 for any polarity of the reading magnetic field.

By such an operation, two temperature domains, i.e. a low temperatureportion and a high temperature portion are masked inside the irradiationdomain of the reading beam, and a double mask type super resolutionmagneto-optical recording medium can be realized, wherein the lowtemperature mask domain and the high temperature mask domain of thereading layer are magnetized in opposite directions, regardless of theinformation stored in the recording layer. In this example, such arecording medium is used, and the reading power has been set in such away that the level of the reading signal is almost the same regardlessof the orientation of the reading magnetic field.

In other words, when the reading power is insufficient, a part of thelow temperature mask portion 2 widens, and the reading output levelswings to the plus side. Conversely, when the reading power isexcessive, a part of the high temperature mask portion 3 widens, and thereading output level swings to the minus side. This phenomenon isinverted if the polarity of the reading magnetic field 9 is reversed. Inthat case, when the reading power is insufficient, a part of the lowtemperature mask portion 2 widens and the reading output level swings tothe minus side, whereas, when the reading power is excessive, a part ofthe high temperature mask portion 3 widens, and the reading output levelswings to the plus side.

A portion of the recording layer 16 is used, where the magnetization isdirected either upwards or downwards. Moreover, the aperture portion 2is positioned in the center of the reading beam irradiation domain 1 anda suitable reading power can be selected so that variations of thereading output level do not occur, even when the reading magnetic fieldis reversed.

Next, reading while applying magnetic fields with opposite polarities atthe beginning and at the end of a recording mark is explained for therecording medium shown in FIG. 17. FIG. 18A shows the transient changeof a reading signal S, FIG. 18B shows the transient change of a readingmagnetic field H.

As can be understood from comparison with the first example shown inFIG. 16, the level variation accompanying the switching of the readingmagnetic field is suppressed, and a reading that correctly responds tothe length of recording marks can be performed just by detecting adownward crossing point or an upward crossing point of slice level S4.

On the other hand, this method is valid for a reading method, in which:in a magnetic super resolution type magneto-optical recording mediumthat attains a signal only from one portion of the irradiation domain ofthe reading beam and has at least a recording layer and a reading layeron a substrate, a focused laser light is irradiated as a reading beamand a magnetic field is modulated, using a magnetic head, which isequipped with a slider and glides or floats on the magnetic superresolution type magneto-optical recording medium; reading is performedwhile impressing a magnetic field in a direction so that at least thetranslation of magnetic domain walls is promoted, and a magnetic fieldis alternated with a period equivalent to less than ½ the shortestwavelength of the recording marks; in one portion of the beamirradiation domain from which the reading signal is attained, magneticfields of two polarities, i.e. a magnetic field with a polarity thataccelerates the transcription of the magnetization of the recordinglayer into the reading layer, and a magnetic field with a polarity thatinhibits the transcription of the magnetization of the recording layerinto the reading layer, are alternatingly impressed with a fixed period.

The present invention as described above brings about the followingeffects:

(1) A correct reading can be performed according to the length ofrecording marks by reading a magneto-optical recording medium whileimpressing a magnetic field with an orientation promoting thetranslation of magnetic domain walls. High density and high transmissionrate become possible.

(2) High density and high transmission rate become possible due toperforming reading while impressing alternatingly with a fixed period,in one portion of the beam irradiation domain from which the readingsignal is attained, magnetic fields of two polarities, i.e. a magneticfield with a polarity that accelerates the transcription of themagnetization of the recording layer into the reading layer, and amagnetic field with a polarity that inhibits the transcription of themagnetization of the recording layer into the reading layer.

(3) High density and high transmission rate become possible becausereading is performed while impressing alternatingly magnetic fields ofdiffering polarities at the end portion and the beginning portion of therecording marks.

(4) It is possible to reduce the magnetic field for recording necessaryfor an initialization by performing a pre-treatment, in which a rangebigger than the domain formed by the recording marks is alreadypolarized on the magneto-optical recording medium in the sameorientation as the initialization at the reading time.

(5) Using a disk-shaped magneto-optical recording medium with positionadjustment having an eccentricity of more than 50 μm, the magnetic headis adjusted into an exact position by observing the reading signal whilethe magnetic head is moved along the surface of the magneto-opticalrecording medium.

(6) Even if the temperature changes after the initialization or tiltoccurs due to humidity variation and the like, it is still possible toperform recording/reading/erasure with the most suitable operation powerby detecting the critical reading power for each sector that constitutesa smallest recording unit.

(7) It is possible to avoid deletion of marks recorded in neighboringtracks, or an increase of cross-talk by determining a suitable recordingpower with a test-writing preceding the recording.

(8) The dissipated can be reduced by reducing driving current of themagnetic head and the laser power during stand-by for reading.

(9) The most suitable reading power can be selected by reading therecorded information while continuously setting the reading power, sothat the reading signal level stays almost the same regardless of theorientation of the reading magnetic field.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, all changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

What is claimed is:
 1. A recording method for a magneto-opticalrecording medium, comprising recording a signal while, according to thesignal to be recorded, a magnetic field is modulated with a magnetichead that is equipped with a slider and glides or floats on a magneticsuper resolution type magneto-optical recording medium that attains asignal only from one portion of an irradiation domain of a reading beam,wherein in an operation to perform a test-writing preceding therecording, a deletion operation is performed by irradiating continuouslight while applying a constant deletion magnetic field, after thedeletion operation, test-writing is performed with a mark pitch that issmaller than a track pitch, while changing the power for recordingthrough light modulation, and a recording power that avoids a conditionof the recording marks resembling overlapping circles is determinedthrough the test-writing.
 2. The recording method for a magneto-opticalrecording medium according to claim 1, wherein information is recordedwith a magnetic field that is modulated according to the information tobe recorded, using a light pulse with a constant period T1 that issynchronized to the clock signal, after the deletion operation, in aconstant magnetic field pointing in the opposite direction of thedeletion magnetic field or in an alternating field with a period T2,where, 2 T1≧T2>T1, the recording is performed through a light pulse witha period T2 which is synchronized to the clock signal, matching thetiming, with which a magnetic field is impressed in the oppositedirection of the deletion magnetic field while the light amount of therecording light pulse is changed, the most suitable light amount issought on the basis of the result of reading, the recording is performedwith the most suitable light amount, using a modulation magnetic fieldcarrying the information to be recorded and a light pulse with theperiod T1.